Pest control is an ongoing, worldwide problem. In addition to physical means of control that have been practiced for centuries, recent decades have witnessed the emergence and widespread use of hundreds of chemically developed pest repellents, growth regulators, and insecticides. These products are frequently synthetic varieties that are heavily refined prior to commercialization—the list includes the pyrethroids (including deltamethrins, cyfluthryns, etc), DEET and other aromatic amides, organophosphates, and carbamates. The usefulness of these products is often limited by factors including human or environmental toxicity, insect resistance (particularly to pyrethroids; see e.g. Romero, et al.), limited dry residue activity, repellancy and physical factors that make them inappropriate for indoor use (odor, staining). For these reasons and due to shifting consumer preference paradigms, there is consistently increasing demand for naturally-derived, effective pest control products that overcome these limitations.
Some pesticide products are derived from botanical and other natural sources; for example the pyrethrin classes of pesticides are derived from the pyrethrum daisy, Chrysanthemum cinerariaefolium. Other examples include: rotenone, from the roots of Derris Lonchocarpus; ryania, from the stems of Ryania speciosa; and neem, derived from the leaves, bark, and seeds of Azadirachta indica. 
The tree Azadirachta indica—in some cases referred to as the “Sacred Tree” or “Nature's Pharmacy”—has long been recognized as a source of a wide variety of useful bioactive compounds. Neem derivatives have demonstrated effectiveness as moisturizing agents, and neem oil itself has been used as a treatment for various skin conditions including acne, psoriasis, and chicken pox. It is also used in toothpastes, as a cooking ingredient, and in pharmaceuticals for treating a range of symptoms including fever, earache, headache, and serious disorders including diabetes (see e.g. Brachmachari). In the agricultural sector, neem oil is considered an effective measure for the prevention of mildew, anthracnose, rust, leaf spot, botrytis, scab and alternaria. Its derivatives have furthermore been described variously as antiviral, antimicrobial, antifungal, and antiseptic. Neem oil and many of its derivatives have also been recognized and used as insect control agents and pesticides.
Neem oil contains dozens of active compounds that kill or repel insects, with demonstrated efficacy against more than 375 insect species. It has been recognized as a repellent of many pests, particularly insects (see e.g. Mishra, et al). At higher concentrations it has been reported to demonstrate repellency activity against some insects for up to six months after application (see Daniel & Smith). These repellency characteristics limit neem oil's insecticidal activity significantly, since insects are repelled from exposure to the very product that is intended to be insecticidal. Neem oil has been shown to prevent egg emergence of some insects when eggs are treated directly with the oil: See Rahman & Talukder; Ahmed, et al. Neem oil also demonstrates some prevention of oviposition—of a limited subset of insects—at higher concentrations (including the maize weevil; see M K Khattak).
Current hypotheses suggest that neem oil may work as a contact killer, as an antifeedant, as an insect-growth regulator, a sterilizing agent, a gut motility inhibitor, and/or as a chitin inhibitor. Azadirachtin —an important active ingredient in neem oil—has been reported to exhibit antifeedant, repellent, and sterilization activities under certain circumstances and has been used as a pest control chemical in the past (see U.S. Pat. No. 4,556,562).
Neem oil and azadirachtin are believed to exhibit complex mechanisms of insect toxicity, including activity upon insect hormonal systems, antifeedant activity, anti-molting activity, and numerous other activities. Neem oil as a pesticide is biodegradable and of low environmental and human toxicity, exempted from the tolerance requirement by the United States EPA (see United States Federal Register, Volume 60, Number 239, 1995).
Neem oil has drawbacks as an insecticide. While effective at preventing molting and exhibiting certain repellency characteristics in some insects, reports of neem oil's knockdown capability are inconsistent (see e.g. Schumutter), and some studies find it less efficient at killing adult insects than related pesticides (see Pavela). Neem oil has been reported to have poor dry residue pesticidal activity against most insects, and poor dry residual prevention of egg emergence and prevention of oviposition against most species of insects. Neem oil has an odor that is offensive to some people, and its odor does not rapidly disperse.
Other natural oils have been reported to exhibit insecticidal or other pest control activities, as are described further below.
Pests are a considerable annoyance and health risk. For example, in recent years, there has been a resurgence of bed bug (Cimex lectularius L.) infestations across North America. Bed bugs cause sleeplessness, anxiety, and discomfort for those affected. Bed bugs are troublesome pests. They live and hide in crevices, seams and other small spaces. They are hard to identify and locate, and can survive dormant for months or a year or more without feeding. They spread by clinging to suitcases, furniture and clothing which people bring with them from place to place. Current methods of bed bug control are expensive and have various limitations, particularly because products must be applied in sleeping areas where the affected individuals are subject to close and lengthy exposure.
There remains a need for improved pesticides derived from natural sources, pesticides that can prevent egg eclosion, and pesticides having improved dry residue and prolonged residual activity.